Lecture 5 Light Quantity, Quality,

1
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• B. Importance of light to humans and other
  organisms

2
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm).
• B. Importance of light to humans and other
  organisms

3
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation.
• B. Importance of light to humans and other
  organisms

4
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation. Colors range
  from violet to blue to green to yellow to orange
  to red.
• B. Importance of light to humans and other
  organisms

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Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation. Colors range
  from violet to blue to green to yellow to orange
  to red.
• B. Importance of light to humans and other
  organisms

7
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation. Colors range
  from violet to blue to green to yellow to orange
  to red.
• B. Importance of light to humans and other
  organisms
• 1. Energy source for photosynthesis in nearly
  all ecosystems.

8
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation. Colors range
  from violet to blue to green to yellow to orange
  to red.
• B. Importance of light to humans and other
  organisms
• 1. Energy source for photosynthesis in nearly
  all ecosystems.
• 2. A cue that environmental conditions will
  soon be changing.

9
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation. Colors range
  from violet to blue to green to yellow to orange
  to red.
• B. Importance of light to humans and other
  organisms
• 1. Energy source for photosynthesis in nearly
  all ecosystems.
• 2. A cue that environmental conditions will
  soon be changing.
• 3. Makes vision possible.

10
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation. Colors range
  from violet to blue to green to yellow to orange
  to red.
• B. Importance of light to humans and other
  organisms
• 1. Energy source for photosynthesis in nearly
  all ecosystems.
• 2. A cue that environmental conditions will
  soon be changing.
• 3. Makes vision possible.
• 4. Plays important role in physiology and
  nutrition.

11
Lecture 5 Light Quantity, Quality, Periodicity

• I. Introduction
• A. What is light (FIG. 1)
• The visible portion of the electromagnetic
  spectrum radiating from the sun. Ranges from
  about 400 nm (0.4 µm) to 700 nm (0.7 µm). Some
  organisms also see UV radiation. Colors range
  from violet to blue to green to yellow to orange
  to red.
• B. Importance of light to humans and other
  organisms
• 1. Energy source for photosynthesis in nearly
  all ecosystems.
• 2. A cue that environmental conditions will
  soon be changing.
• 3. Makes vision possible.
• 4. Plays important role in physiology and
  nutrition.
• Well look at the role of light as an energy
  source and a cue.

12
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• B. Light absorption by leaves (FIG. 2)
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

13
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis.
• B. Light absorption by leaves (FIG. 2)
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

14
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

17
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths.
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  ____ and ____.
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  blue and red.
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

22
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  blue and red. The most important molecules
  absorbing the blue and red wavelengths are ____
  and ______ molecules.
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

23
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  blue and red. The most important molecules
  absorbing the blue and red wavelengths are
  chlorophyll and carotenoid molecules.
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• A. Photosynthetically active radiation
  (PAR)(FIG. 1)
• PAR the solar radiation wavelengths that
  provide energy for photosynthesis. These are
  the same wavelengths as visible light!
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  blue and red. The most important molecules
  absorbing the blue and red wavelengths are
  chlorophyll and carotenoid molecules.
  Chlorophylls absorb mostly blue red and
  therefore reflect ____. Carotenoids absorb blue
  some green and therefore reflect mostly____.
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

26
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  blue and red. The most important molecules
  absorbing the blue and red wavelengths are
  chlorophyll and carotenoid molecules.
  Chlorophylls absorb mostly blue red and
  therefore reflect green. Carotenoids absorb blue
  some green and therefore reflect mostly red.
• C. Light extinction (attenuation)(FIG. 3)
• D. Light response curves
• E. Shade tolerance of plants

27
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  blue and red. The most important molecules
  absorbing the blue and red wavelengths are
  chlorophyll and carotenoid molecules.
  Chlorophylls absorb mostly blue red and
  therefore reflect green. Carotenoids absorb blue
  some green and therefore reflect mostly red.
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction?

28
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• B. Light absorption by leaves (FIG. 2)
• Action spectrum for photosynthesis is the
  relative photosynthesis rate when plants are
  given light of specific wavelengths. The most
  important wavelengths for photosynthesis are
  blue and red. The most important molecules
  absorbing the blue and red wavelengths are
  chlorophyll and carotenoid molecules.
  Chlorophylls absorb mostly blue red and
  therefore reflect green. Carotenoids absorb blue
  some green and therefore reflect mostly red.
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction? Reduction in
  light levels under plants as light is
  absorbed and reflected by leaves.

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction? Reduction in
  light levels under plants as light is
  absorbed and reflected by leaves. Therefore many
  plants in nature dont have much light.

31
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction? Reduction in
  light levels under plants as light is
  absorbed and reflected by leaves. Therefore many
  plants in nature dont have much light. The
  quality of light is also changed under a
  plant canopy--more green relative to the amount
  of red.

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction? Reduction in
  light levels under plants as light is
  absorbed and reflected by leaves. Therefore many
  plants in nature dont have much light. The
  quality of light is also changed under a
  plant canopy--more green relative to the amount
  of red.
• 2. Leaf area index (LAI)

34
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction? Reduction in
  light levels under plants as light is
  absorbed and reflected by leaves. Therefore many
  plants in nature dont have much light. The
  quality of light is also changed under a
  plant canopy--more green relative to the amount
  of red.
• 2. Leaf area index (LAI)
• LAI the number of layers of leaves above
  a point on the ground.

35
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction? Reduction in
  light levels under plants as light is
  absorbed and reflected by leaves. Therefore many
  plants in nature dont have much light.
  The quality of light is also is also
  changed under a plant canopy--more green relative
  to the amount of red.
• 2. Leaf area index (LAI)
• LAI the number of layers of leaves above
  a point on the ground.
• 3. Beer-Lambert Law

36
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 1. What is light extinction? Reduction in
  light levels under plants as light is
  absorbed and reflected by leaves. Therefore many
  plants in nature dont have much light. The
  quality of light is also changed under a
  plant canopy--more green relative to the amount
  of red.
• 2. Leaf area index (LAI)
• LAI the number of layers of leaves above
  a point on the ground.
• 3. Beer-Lambert Law
• I/Io e -k(LAI) where I PAR on the
  ground
• Io PAR at top of plant canopy
• k extinction coefficient
  LAI leaf area index

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 3. Beer-Lambert Law
• I/Io e -k(LAI) where I PAR on
  the ground
• Io PAR at top of plant canopy
• k extinction coefficient
  (opacity, orientation)
  LAI leaf area index
• 4. Examples
• a. Field of green grass (LAI 5, k 0.4)
• b. Typical garden (LAI 5, k 0.8)

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 4. Examples
• a. Field of green grass (LAI 5, k 0.4)
• I/Io e -(0.45) e -2
  0.135 13.5 of light penetrates grass.
• b. Typical garden (LAI 5, k 0.8)

39
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 4. Examples
• a. Field of green grass (LAI 5, k 0.4)
• I/Io e -(0.45) e -2 0.135
  13.5 of light penetrates grass.
• b. Typical garden (LAI 5, k 0.8)
• I/Io e -(0.85) e -4 0.018 1.8
  of light penetrates garden.

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 4. Examples
• a. Field of green grass (LAI 5, k 0.4)
• I/Io e -(50.4) e -2 0.135
  13.5 of light penetrates grass.
• b. Typical garden (LAI 5, k 0.8)
• I/Io e -(50.8) e -4 0.018 1.8
  of light penetrates garden.
• k is lower for grass because upright
  leaves allow light through.

41
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 4. Examples
• a. Field of green grass (LAI 5, k 0.4)
• I/Io e -(50.4) e -2 0.135
  13.5 of light penetrates grass.
• b. Typical garden (LAI 5, k 0.8)
• I/Io e -(50.8) e -4 0.018 1.8
  of light penetrates garden.
• k is lower for grass because upright
  leaves allow light through.
• 5. Seasonal changes in light extinction in a
  deciduous forest (FIG. 4)

42
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 4. Examples
• a. Field of green grass (LAI 5, k 0.4)
• I/Io e -(50.4) e -2 0.135
  13.5 of light penetrates grass.
• b. Typical garden (LAI 5, k 0.8)
• I/Io e -(50.8) e -4 0.018 1.8
  of light penetrates garden.
• k is lower for grass because upright
  leaves allow light through.
• 5. Seasonal changes in light extinction in a
  deciduous forest (FIG. 4)
• Even under dense forests, some plants can
  grow. How?

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 4. Examples
• a. Field of green grass (LAI 5, k 0.4)
• I/Io e -(50.4) e -2 0.135
  13.5 of light penetrates grass.
• b. Typical garden (LAI 5, k 0.8)
• I/Io e -(50.8) e -4 0.018 1.8
  of light penetrates garden.
• k is lower for grass because upright
  leaves allow light through.
• 5. Seasonal changes in light extinction in a
  deciduous forest (FIG. 4)
• Even under dense forests, some plants can
  grow. How? In deciduous forests there is
  a window of opportunity each year.

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46
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 5. Seasonal changes in light extinction in a
  deciduous forest (FIG. 4)
• Even under dense forests, some plants can
  grow. How? In deciduous forests
  there is a window of opportunity each year.
  Light levels on the forest floor are highest in
  the spring when sun has more energy than in
  winter but there are no leaves on the trees.

47
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 5. Seasonal changes in light extinction in a
  deciduous forest (FIG. 4)
• Even under dense forests, some plants can
  grow. How? In deciduous forests
  there is a window of opportunity each year.
  Light levels on the forest floor are highest in
  the spring when sun has more energy than in
  winter but there are no leaves on the trees.
  Many vernal herbs grow, flower, and produce
  fruit in the spring.

48
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• C. Light extinction (attenuation)(FIG. 3)
• 5. Seasonal changes in light extinction in a
  deciduous forest (FIG. 4)
• Even under dense forests, some plants can
  grow. How? In deciduous forests
  there is a window of opportunity each year.
  Light levels on the forest floor are highest in
  the spring when sun has more energy than in
  winter but there are no leaves on the trees.
  Many vernal herbs grow, flower, and produce
  fruit in the spring.
• D. Light response curves (FIG. 5)
• E. Shade tolerance in plants

49
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions.

50
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions. This can be seen by
  providing different amounts of light and
  measuring net photosynthesis (light response
  curves).

51
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions. This can be seen by
  providing different amounts of light and
  measuring net photosynthesis (light response
  curves).
• 1. Compensation point
• 2. Saturation point
• 3. Dark respiration rate
• 4. Photoinhibition

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions. This can be seen by
  providing different amounts of light and
  measuring net photosynthesis (light response
  curves).
• 1. Compensation point - minimum PAR required
  for positive net ps
• 2. Saturation point
• 3. Dark respiration rate
• 4. Photoinhibition

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions. This can be seen by
  providing different amounts of light and
  measuring net photosynthesis (light response
  curves).
• 1. Compensation point - minimum PAR required
  for positive net ps
• 2. Saturation point - maximum PAR that plant
  can use for ps
• 3. Dark respiration rate
• 4. Photoinhibition

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57
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions. This can be seen by
  providing different amounts of light and
  measuring net photosynthesis (light response
  curves).
• 1. Compensation point - minimum PAR required
  for positive net ps
• 2. Saturation point - maximum PAR that plant
  can use for ps
• 3. Dark respiration rate - estimated as net ps
  at night or in deep shade
• 4. Photoinhibition

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions. This can be seen by
  providing different amounts of light and
  measuring net photosynthesis (light response
  curves).
• 1. Compensation point - minimum PAR required
  for positive net ps.
• 2. Saturation point - maximum PAR that plant
  can use for ps.
• 3. Dark respiration rate - estimated as net ps
  at night or in deep shade.
• 4. Photoinhibition - reduced net ps at very
  high light levels due to heat and reactive
  oxygen molecules (oxidation) that damage
  chlorophyll.

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• D. Light response curves (FIG. 5). Many other
  plants can survive in shade because they are
  adapted to dark conditions. This can be seen by
  providing different amounts of light and
  measuring net photosynthesis (light response
  curves).
• 1. Compensation point - minimum PAR required
  for positive net ps.
• 2. Saturation point - maximum PAR that plant
  can use for ps.
• 3. Dark respiration rate - estimated as net ps
  at night or in deep shade.
• 4. Photoinhibition - reduced net ps at very
  high light levels due to heat and reactive
  oxygen molecules (oxidation) that damage
  chlorophyll.
• E. Shade tolerance in plants

62
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• 2. What are the mechanisms of shade
  tolerance?
• 3. Characteristics of shade-intolerant
  species shade-tolerant species

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• Ability to maintain positive net
  photosynthesis in low light.
• 2. What are the mechanisms of shade
  tolerance?
• 3. Characteristics of shade-intolerant
  species shade-tolerant species

64
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• Ability to maintain positive net
  photosynthesis in low light.
• 2. What are the mechanisms of shade
  tolerance?
• a. Physiological changes (FIG. 6)
• b. Morphological changes (FIG. 7)
• 3. Characteristics of shade-intolerant
  species shade-tolerant species

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• Ability to maintain positive net
  photosynthesis in low light.
• 2. What are the mechanisms of shade
  tolerance?
• a. Physiological changes (FIG. 6)
• Must allocate resources efficiently
  to maximize net ps.
• b. Morphological changes (FIG. 7)
• 3. Characteristics of shade-intolerant
  species shade-tolerant species

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• Ability to maintain positive net
  photosynthesis in low light.
• 2. What are the mechanisms of shade
  tolerance?
• a. Physiological changes (FIG. 6)
• Must allocate resources efficiently
  to maximize net ps. Allocate
  most N and other resources to build chlorophyll
  and carotenoid molecules rather than
  Calvin cycle enzymes.
• b. Morphological changes (FIG. 7)
• 3. Characteristics of shade-intolerant
  species shade-tolerant species

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• Ability to maintain positive net
  photosynthesis in low light.
• 2. What are the mechanisms of shade
  tolerance?
• a. Physiological changes (FIG. 6)
• Must allocate resources efficiently
  to maximize net ps. Allocate
  most N and other resources to build chlorophyll
  and carotenoid molecules rather than
  Calvin cycle enzymes.
• b. Morphological changes (FIG. 7).
  Again, a matter of efficient resource
  allocation.

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Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• Ability to maintain positive net
  photosynthesis in low light.
• 2. What are the mechanisms of shade
  tolerance?
• a. Physiological changes (FIG. 6)
• Must allocate resources efficiently
  to maximize net ps. Allocate
  most N and other resources to build chlorophyll
  and carotenoid molecules rather than
  Calvin cycle enzymes.
• b. Morphological changes (FIG. 7).
  Again, a matter of efficient resource
  allocation. Four organs in plant leaves, stems,
  roots, and flowers/fruits. Plants in
  shade allocate most to ____.

70
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 1. What is shade tolerance?
• Ability to maintain positive net
  photosynthesis in low light.
• 2. What are the mechanisms of shade
  tolerance?
• a. Physiological changes (FIG. 6)
• Must allocate resources efficiently
  to maximize net ps. Allocate
  most N and other resources to build chlorophyll
  and carotenoid molecules rather than
  Calvin cycle enzymes.
• b. Morphological changes (FIG. 7).
  Again, a matter of efficient resource
  allocation. Four organs in plant leaves, stems,
  roots, and flowers/fruits. Plants in
  shade allocate most to leaves.

71
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 2. What are the mechanisms of shade
  tolerance?
• a. Physiological changes (FIG. 6)
• Must allocate resources efficiently
  to maximize net ps. Allocate
  most N and other resources to build chlorophyll
  and carotenoid molecules rather than
  Calvin cycle enzymes.
• b. Morphological changes (FIG. 7).
  Again, a matter of efficient resource
  allocation. Four organs in plant leaves, stems,
  roots, and flowers/fruits. Plants in
  shade allocate most to leaves. They
  also make thinner leaves to capture more light
  with the same resources.

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73
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 3. Characteristics of shade-intolerant
  species shade-tolerant species
• a. Shade-intolerant species
• b. Shade-tolerant species

74
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 3. Characteristics of shade-intolerant
  species shade-tolerant species
• a. Shade-intolerant species - high
  photosynthesis and respiration rates,
  high light compensation and saturation points.
  Thrive in open, disturbed conditions
  but not in shade. Profligate strategy.
• b. Shade-tolerant species

75
Lecture 5 Light Quantity, Quality, Periodicity

• II. The Role of Light in Photosynthesis
• E. Shade tolerance in plants
• 3. Characteristics of shade-intolerant
  species shade-tolerant species
• a. Shade-intolerant species - high
  photosynthesis respiration rates,
  high light compensation saturation points.
  Thrive in open, disturbed conditions
  but not in shade. Profligate strategy.
• b. Shade-tolerant species - low
  photosynthesis respiration rates,
  low light compensation saturation points. Grow
  slowly. Cant compete on open sites
  but can survive in shade and on
  undisturbed sites. Conservative (miserly)
  strategy.

76
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• B. Examples

77
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness.
• B. Examples

78
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness. Innate instinctive, independent of
  environment.
• B. Examples

79
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness. Innate instinctive, independent of
  environment.
• B. Examples
• Diurnal organisms -
• Nocturnal organism -

80
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness. Innate instinctive, independent of
  environment.
• B. Examples
• Diurnal organisms - most plants, many birds,
  mammals, invertebrates
• Nocturnal organism -

81
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness. Innate instinctive, independent of
  environment.
• B. Examples
• Diurnal organisms - most plants, many birds,
  mammals, invertebrates
• Nocturnal organism - foxes, raccoons, owls,
  bats, rodents, hawkmoths

82
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness. Innate instinctive, independent of
  environment.
• B. Examples
• Diurnal organisms - most plants, many birds,
  mammals, invertebrates
• Nocturnal organism - foxes, raccoons, owls,
  bats, rodents, hawkmoths
• C. How do we know that daily patterns are
  innate? (FIG. 8)

83
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness. Innate instinctive, independent of
  environment.
• B. Examples
• Diurnal organisms - most plants, many birds,
  mammals, invertebrates
• Nocturnal organism - foxes, raccoons, owls,
  bats, rodents, hawkmoths
• C. How do we know that daily patterns are
  innate? (FIG. 8)
• If animals are deprived of light, patterns are
  maintained in a free- running cycle.

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85
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• A. What are circadian rhythms?
• Innate patterns of daily activities that
  correspond to 24-hour cycles of light and
  darkness. Innate instinctive, independent of
  environment.
• B. Examples
• Diurnal organisms - most plants, many birds,
  mammals, invertebrates
• Nocturnal organism - foxes, raccoons, owls,
  bats, rodents, hawkmoths
• C. How do we know that daily patterns are
  innate? (FIG. 8)
• If animals are deprived of light, patterns are
  maintained in a free- running cycle. However,
  the cycle gradually drifts away from a 24- hour
  cycle and may become erratic. Circadian rhythms
  are innate but are entrained by external cues.

86
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• C. How do we know that daily patterns are
  innate? (FIG. 8)
• If animals are deprived of light, patterns are
  maintained in a free- running cycle. However,
  the cycle gradually drifts away from a 24- hour
  cycle and may become erratic. Circadian rhythms
  are innate but are entrained by external cues.
• D. The light detector (biological clock) in
  organisms
• 1. Plants
• 2. Insects
• 3. Birds and reptiles
• 4. Mammals

87
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• C. How do we know that daily patterns are
  innate? (FIG. 8)
• If animals are deprived of light, patterns are
  maintained in a free- running cycle. However,
  the cycle gradually drifts away from a 24- hour
  cycle and may become erratic. Circadian rhythms
  are innate but are entrained by external cues.
• D. The light detector (biological clock) in
  organisms
• 1. Plants - phytochrome (protein) has two
  forms. During the day Pr absorbs red light
  and converts to Pfr, which triggers growth,
  flowering, etc.
• 2. Insects
• 3. Birds and reptiles
• 4. Mammals

88
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• C. How do we know that daily patterns are
  innate? (FIG. 8)
• If animals are deprived of light, patterns are
  maintained in a free- running cycle. However,
  the cycle gradually drifts away from a 24- hour
  cycle and may become erratic. Circadian rhythms
  are innate but are entrained by external cues.
• D. The light detector (biological clock) in
  organisms
• 1. Plants - phytochrome (protein) has two
  forms. During the day Pr absorbs red light
  and converts to Pfr, which triggers growth,
  flowering, etc. At night, Pfr absorbs far-red
  light (no red light available) and converts
  to Pr, which stops growth, etc.
• 2. Insects
• 3. Birds and reptiles
• 4. Mammals

89
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 1. Plants - phytochrome (protein) has two
  forms. During the day Pr absorbs red light
  and converts to Pfr, which triggers growth,
  flowering, etc. At night, Pfr absorbs far-red
  light (no red light available) and converts
  to Pr, which stops growth, etc.
• 2. Insects - most have receptor at base of
  compound eyes that connects by axons to
  clock in the brain.
• 3. Birds and reptiles
• 4. Mammals

90
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 1. Plants - phytochrome (protein) has two
  forms. During the day Pr absorbs red light
  and converts to Pfr, which triggers growth,
  flowering, etc. At night, Pfr absorbs far-red
  light (no red light available) and converts
  to Pr, which stops growth, etc.
• 2. Insects - most have receptor at base of
  compound eyes that connects by axons to
  clock in the brain.
• 3. Birds and reptiles - clock located in
  pineal gland near surface of lower central
  brain.
• 4. Mammals

91
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 1. Plants - phytochrome (protein) has two
  forms. During the day Pr absorbs red light
  and converts to Pfr, which triggers growth,
  flowering, etc. At night, Pfr absorbs far-red
  light (no red light available) and converts
  to Pr, which stops growth, etc.
• 2. Insects - most have receptor at base of
  compound eyes that connects by axons to
  clock in the brain.
• 3. Birds and reptiles - clock located in
  pineal gland near surface of lower central
  brain.
• 4. Mammals - two clumps of neurons near
  intersection of optic nerves as they leave
  the eyes. Hormone melatonin operates the
  clock, but hypothalamus is the regulator.

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Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 4. Mammals - two clumps of neurons near
  intersection of optic nerves as they leave
  the eyes. Hormone melatonin operates the
  clock, but hypothalamus is the regulator.
• Summary many different organisms have a
  clock but the physiological mechanism is
  very different.

93
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 4. Mammals - two clumps of neurons near
  intersection of optic nerves as they leave
  the eyes. Hormone melatonin operates the
  clock, but hypothalamus is the regulator.
• Summary many different organisms have a
  clock but the physiological mechanism is
  very different.
• E. What is the adaptive value of circadian
  rhythms?

94
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 4. Mammals - two clumps of neurons near
  intersection of optic nerves as they leave
  the eyes. Hormone melatonin operates the
  clock, but hypothalamus is the regulator.
• Summary many different organisms have a
  clock but the physiological mechanism is
  very different.
• E. What is the adaptive value of circadian
  rhythms?
• Prepare organisms for changes in physical or
  biological environment.

95
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 4. Mammals - two clumps of neurons near
  intersection of optic nerves as they leave
  the eyes. Hormone melatonin operates the
  clock, but hypothalamus is the regulator.
• Summary many different organisms have a
  clock but the physiological mechanism is
  very different.
• E. What is the adaptive value of circadian
  rhythms?
• Prepare organisms for changes in physical or
  biological environment.
• Physical - lower temp, increased RH in evening
  good for flying insects.

96
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• D. The light detector (biological clock) in
  organisms
• 4. Mammals - two clumps of neurons near
  intersection of optic nerves as they leave
  the eyes. Hormone melatonin operates the
  clock, but hypothalamus is the regulator.
• Summary many different organisms have a
  clock but the physiological mechanism is
  very different.
• E. What is the adaptive value of circadian
  rhythms?
• Prepare organisms for changes in physical or
  biological environment.
• Physical - lower temp, increased RH in evening
  good for flying insects. Biological - open
  flowers in day provide food for pollinators and
  increased rodent activity at night provides prey
  for owls, cats.

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Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• E. What is the adaptive value of circadian
  rhythms?
• Prepare for changes in physical or biological
  environment.
• Physical - lower temp, increased RH in evening
  good for flying insects. Biological - open
  flowers in day provide food for pollinators and
  increased rodent activity at night provides prey
  for owls, cats.
• F. Other types of rhythms in organisms (FIG. 9)
  

98
Lecture 5 Light Quantity, Quality, Periodicity

• III. Circadian Rhythms
• E. What is the adaptive value of circadian
  rhythms?
• Prepare for changes in physical or biological
  environment.
• Physical - lower temp, increased RH in evening
  good for flying insects. Biological - open
  flowers in day provide food for pollinators and
  increased rodent activity at night provides prey
  for owls, cats.
• F. Other types of rhythms in organisms (FIG. 9)
• Fiddler crab has circadian rhythm for color
  changes and tidal rhythm to determine active
  period. Requires multiple clocks!

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100
Lecture 5 Light Quantity, Quality, Periodicity

• IV. Photoperiod
• A. What is photoperiodism?
• B. Adaptive value of photoperiodism
• C. Examples

101
Lecture 5 Light Quantity, Quality, Periodicity

• IV. Photoperiod
• A. What is photoperiodism?
• Response to changing daylength throughout the
  year.
• B. Adaptive value of photoperiodism
• C. Examples

102
Lecture 5 Light Quantity, Quality, Periodicity

• IV. Photoperiod
• A. What is photoperiodism?
• Response to changing daylength throughout the
  year. Important for most organisms except those
  living near the _______.
• B. Adaptive value of photoperiodism
• C. Examples

103
Lecture 5 Light Quantity, Quality, Periodicity

• IV. Photoperiod
• A. What is photoperiodism?
• Response to changing daylength throughout the
  year. Important for most organisms except those
  living near the equator.
• B. Adaptive value of photoperiodism
• C. Examples

104
Lecture 5 Light Quantity, Quality, Periodicity

• IV. Photoperiod
• A. What is photoperiodism?
• Response to changing daylength throughout the
  year. Important for most organisms except those
  living near the equator.
• B. Adaptive value of photoperiodism
• The most reliable cue of upcoming seasonal
  changes in the environment.
• C. Examples

105
Lecture 5 Light Quantity, Quality, Periodicity

• IV. Photoperiod
• A. What is photoperiodism?
• Response to changing daylength throughout the
  year. Important for most organisms except those
  living near the equator.
• B. Adaptive value of photoperiodism
• The most reliable cue of upcoming seasonal
  changes in the environment.
• C. Examples
• Flowering long-day plants (lettuce, spinach,
  potatoes)
• short-day plants (strawberries,
  chrysanthemum)

106
Lecture 5 Light Quantity, Quality, Periodicity

• IV. Photoperiod
• A. What is photoperiodism?
• Response to changing daylength throughout the
  year. Important for most organisms except those
  living near the equator.
• B. Adaptive value of photoperiodism
• The most reliable cue of upcoming seasonal
  changes in the environment.
• C. Examples
• Flowering long-day plants (lettuce, spinach,
  potatoes)
• short-day plants (strawberries,
  chrysanthemum)
• Birds migrating between breeding